Turning machines for machining bar-shaped semi-finished products, which will be referred to below as material bars, are principally known and usually comprise a stationary or traversable headstock, in which one or more spindles driven by a drive unit are supported along a z axis that extends along the introduction or conveying direction of the material bars. In the processing area of the turning machine, the material bar clamped in the spindle of the turning machine is machined using a tool. To this end, the material bar is usually introduced from the rear headstock side of the turning machine into the rotary spindle thereof, which is formed as a hollow shaft, and is clamped therein using a chuck so as to be machined.
Bar loading magazines, which are also referred to as loading magazines or as bar loaders, are also principally known and allow the guiding of material bars on these turning machines. A bar loading magazine provided on a turning machine has to guide the material bar during the entire machining process as precisely as possible, in order to avoid vibrations and oscillations on the turning machine and the bar loading magazine.
When trying to avoid vibrations and/or oscillations, it is above all the support and guidance of the material bar in the bar loading magazine that is of particular importance, and a number of different requirements with regard to dimensions and geometries of the material bars have to be taken into account. Thus, as a rule the material bars have lengths of up to 6 m and diameters between 1 mm and 100 mm. Further, the material bars may have the most varied cross-sectional profiles, wherein symmetrical and unsymmetrical cross-sectional profiles have to be distinguished.
Further, the support and guidance of the material bars in the bar loading machine has to meet the most varied requirements in order to allow an economical and productive manufacturing process to take place. In this regard, often also high rotary speeds of up to 15,000 rpm for machining the material bars to be machined in a rotary manner as well as their orientation in the rotary spindle of the turning machine have to be involved. Thus, a centric or eccentric clamping in the rotary spindle of the turning machine has to be considered for material bars that have to be machined in a rotary manner, and for this reason imbalances due to an uneven mass distribution about the rotary axis about which the material bar is rotated during the rotary machining may occur, and for this reason high requirements have to be met by the guiding mechanism of the bar loading magazine, in order to be able to maintain the required manufacturing tolerances.
From DE 10 2011 015 578 A1, for example supporting and guiding units are known which can be traversed within the bar loading magazine along the z axis and are equipped for supporting and guiding the material bars e.g. using bushes, into which the material bars can be introduced in the longitudinal direction and also along the z axis. Further, a supporting and guiding unit suitable for this purpose, i.e. for supporting a material bar received by the guiding unit in relation to its radial orientation and to guide it along its longitudinal direction, has to allow a rotation of the material bar. For the sake of simplification, such a supporting and guiding unit will be defined below as a guiding unit.
In DE 10 2011 015 578 A1, the bushes used for such a guiding unit are rotationally supported for this purpose within a bush unit, and usually also a plurality of bush units may be positioned at a distance from each other, in particular evenly spaced from each other, along the z axis, so as to be able to avoid oscillations as far as possible.
Apart from the standardised profiles such as circular, square or hexagonal profiles or tube profiles, which have a profile that is substantially symmetrical about the longitudinal orientation thereof, there are also asymmetrical profiles, such as e.g. a so-called lock profile. This type of profile is already designed to have an often even continuous asymmetry of the profile bar cross section in relation to the longitudinal direction thereof over the entire profile length in the direction of the longitudinal axis.
Thus, during the machining of rotating material bars, as a rule an undesirable imbalance develops as a result of the rotation of unequally distributed masses. This imbalance is caused in a more or less pronounced manner e.g. by uneven material inclusions, inaccurate manufacturing or clamping of the material bars or even due to intentionally unsymmetrical profiles, such as e.g. in the case of the lock profile. In particular in the case of intentionally unsymmetrical profiles, the rotary processing will as a rule not be carried out in the centroid of the profile, i.e. during the rotary machining, the rotary axis is eccentric in relation to the main axis of inertia of the material bar along the longitudinal direction thereof, and any imbalance occurring here during rotation will therefore cause vibrations. However, also in the case of inaccuracies due to manufacturing, e.g. in the case of uneven material inclusions or in the case of a less than absolute straightness of the material bar, as well as in the case of an inaccurate clamping of the material bar in relation to the main axis of inertia of the material bar along the longitudinal direction thereof, any imbalance occurring here during rotation will therefore, in particular in the case of high rotary speeds, lead to substantial vibrations.
Such imbalances are especially undesirable in particular also because finished work pieces are cut off from the material bars, because due to this cutting off, the imbalances of the material bar lengths to be guided on the turning machines are subject to continuous change. Further, with each advance movement of the material bar in the introduction or conveying direction in the bar loading magazine, a further imbalance may be added as a function of the advance movement.
For counteracting any imbalance in a rotating body made from a hard and brittle material, which is technologically difficult to machine, patent document DD 245 934 A1 describes a design with a balancing weight and an associated recess in the rotating body. The balancing weight is here placed, during standstill, along a circular groove in any desired position on the circumference of the rotating body and is subsequently clamped using a screw. Consequently, such a design is not suitable for the balancing of continuously changing imbalances as may occur whilst guiding material bars on a turning machine.
For counteracting an imbalance on a component rotating about a rotary axis, on which an imbalance may occur during manufacturing or during use, DE 10 2012 216 867 A1 describes a design, according to which the component comprises a balancing element that is artificially introduced or fixed to be stationary, which protrudes from the component in such a way that it is suitable, during continuous rotation about the rotary axis, for cutting off individual pieces and wherein the balancing element is provided in such a place that it contributes to reducing the imbalance during the removal. Such a design, too, is consequently not suitable for balancing continuously changing imbalances as may occur during the guiding of material bars on a turning machine.
DE 10 2008 027 327 describes a device for automatically balancing a rotating machine part with at least one imbalance compensation disk that has at least one annular cavity provided concentrically to the rotary axis of the machine part. In this cavity, freely movable compensation elements are provided which compensate any imbalance by adopting a counter-position and which are formed as ball rollers with two symmetrically flattened end sides. Consequently, in the case of continuously changing imbalances as may occur during the guiding of material bars on a turning machine, there is a risk of an unstable system with increasing vibrations.
DD 270 136 A1 describes an apparatus for balancing a rotating system, such as e.g. a servo track writing spindle with clamped-on magnetic storage disks prior to recording the servo track, during rotation by means of a plurality of magnetic compensation masses that can be moved in a rolling manner in a co-rotating concentric annular chamber. Here, the rolling compensation masses can, whilst the system is running up, automatically always adopt the same predefined starting position. Subsequently, a positioning unit generates a localised rotating magnetic field that brings the compensation masses, one after another, once into a pre-calculated compensation position, whereupon the magnetic field and the positioning unit are switched off. Consequently, such a design is not suitable for balancing continuously changing imbalances as may occur during the guiding of material bars on a turning machine either.